The present invention relates generally to an apparatus for supporting and distributing the load in a downhole tool. More particularly, the present invention relates to extreme service applications, employing a two slot-and-pin engagement, a high pressure permanent packer, and a plurality of slip elements that distribute the load across many points on the casing, thereby lowering the localized stress on the casing wall and reducing the chance of failure.
Once a petroleum well has been drilled and cased, it is often necessary or desired to drill one or more additional wells that branch off, or deviate, from the first well. Such multilateral wells are typically directed toward different parts of the surrounding formation, with the intent of increasing the output of the well. Because the location.of the target formation typically falls-within a known azimuthal range, it is desirable to control the initial orientation of the deviation fairly precisely.
In order to drill a new borehole that extends outside an existing cased wellbore, the usual practice is to use a work string to run and set an anchored whipstock. The upper end of the whipstock comprises an inclined face. The inclined face guides a window milling bit laterally with respect to the casing axis as the bit is lowered, so that it cuts a window in the casing. The lower end of the whipstock is adapted to engage the anchor in a locking manner that prevents both axial and rotation movement.
It has been found that conventional whipstock supports may be susceptible to small but not insignificant amounts of rotational movement. Hence, it is desired to provide an anchor and whipstock setting apparatus that effectively prevent the whipstock from rotating. It is further desired to provide a system that can set the packer and anchor the whipstock in a single trip. It is further desired to provide an effective whipstock support that can be run in and set using conventional wireline methods.
Furthermore, in prior art devices, disengagement of the whipstock from the orienting key is typically prevented by a shear pin or similar device. The load capacity of this device limits the amount of load that can be placed on the tool. Hence, it is further desired to provide a key element that resists unintentional disengagement while allowing a greater downhole load to be supported by the tool.
In extreme service applications, such as high pressure environments (defined herein as pressures greater than 15,000 psia), it has been found that when conventional anchor slip arrangements are used, the load is distributed against the casing through the slips in such a way that the casing may fail. Hence, it is desired to provide an anchor slip arrangement that reduces the risk of this type of casing failure.
In addition, relative rotation of the components of prior art devices is typically resisted by a key or straight spline. The separation of duties (resisting torsional movement, resisting axial movement and orienting) in the prior art, and the performance these duties by separate mechanisms resulted in a tool that was relatively complex and susceptible to a variety of failure modes. Hence, it is desirable to provide a tool that combines performance of these duties in single, robust device.
On embodiment of the present invention provides an anchor and whipstock setting apparatus that effectively prevents the whipstock from rotating. In this embodiment, the tool includes a frangible slip ring that includes a tongue-and-groove interface with the bottom sub of the tool, so as to resist rotation about the tool axis when the slips engage the casing.
The present invention further provides a key, or scoop, that resists unintentional disengagement of the stinger from the key element. The preferred scoop includes a two part locking device that includes at least one, and preferably at least three, pin engaging slots. The preferred scoop comprises inner and outer concentric tubular members, each including at least one pin engaging slot. In this manner, the key element provides a single orientation, while simultaneously providing axial support at multiple points around the azimuth of the tool and allowing greater loads to be supported.
In some embodiments, the present invention provides an apparatus that allows anchoring and orienting a whipstock in a well casing on a single trip of a running string into and out of the casing or using two trips with wireline tools.
In extreme service applications, such as high pressure environments, an alternative embodiment of the present invention may be employed, comprising a double slot-and-pin locking engagement, a high pressure permanent packer, and a plurality of slip elements of equal axial length that distribute the load across many points on the casing.